package org.tigris.scarab.util;

/* ================================================================
 * Copyright (c) 2000-2002 CollabNet.  All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 * 
 * 1. Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 * 
 * 2. Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the distribution.
 * 
 * 3. The end-user documentation included with the redistribution, if
 * any, must include the following acknowlegement: "This product includes
 * software developed by Collab.Net <http://www.Collab.Net/>."
 * Alternately, this acknowlegement may appear in the software itself, if
 * and wherever such third-party acknowlegements normally appear.
 * 
 * 4. The hosted project names must not be used to endorse or promote
 * products derived from this software without prior written
 * permission. For written permission, please contact info@collab.net.
 * 
 * 5. Products derived from this software may not use the "Tigris" or 
 * "Scarab" names nor may "Tigris" or "Scarab" appear in their names without 
 * prior written permission of Collab.Net.
 * 
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL COLLAB.NET OR ITS CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
 * IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * ====================================================================
 * 
 * This software consists of voluntary contributions made by many
 * individuals on behalf of Collab.Net.
 */ 

import java.util.Collections;
import java.util.Iterator;
import java.util.NoSuchElementException;

public class SubsetIterator 
    implements Iterator
{
    public static final SubsetIterator EMPTY = new EmptySubsetIterator();

    private Iterator i;
    private final int offset;
    private final int elements;
    private int currentPosition;
    
    /**
     * Constructs an itarator on a subset of the given iterator.
     * The SubsetIterator starts with the offset-element and iterates
     * over <code>elements</code> elements
     * 
     * @param i      the Iterator to subset
     * @param offset the position of the first element of the subset
     * @param element  the number of elements the subset should have. 
     */
    public SubsetIterator(Iterator i, int offset, int elements)
    {
     
        this.i = i;
        this.offset = offset;
        this.elements = elements;
        currentPosition = 0;
    }

    /**
     * Constructs an itarator on a subset of the given iterator.
     * The SubsetIterator starts with the offset-element and iterates
     * over all elements
     * 
     * @param i      the Iterator to subset
     * @param offset the position of the first element of the subset
     */
    public SubsetIterator(Iterator i, int offset)
    {
        this(i, offset, Integer.MAX_VALUE);
    }
    
    private Boolean hasNext;
    public boolean hasNext()
    {
        if (hasNext == null) 
        {
            hasNext = (internalIterate()) 
                ? Boolean.TRUE : Boolean.FALSE;
        }
        return hasNext.booleanValue();
    }

    boolean firstCall = true;
    private boolean internalIterate()
    {
        if (firstCall) 
        {
            for (int m = 0; i.hasNext() && m < offset; m++) 
            {
                i.next();
            }
            firstCall = false;
        }
        currentPosition++;
        return i.hasNext() && currentPosition <= elements;
    }

    public Object next()
    {
        if (hasNext()) 
        {
            hasNext = null;
            return i.next();
        }
        else 
        {
            throw new NoSuchElementException("Iterator is exhausted"); //EXCEPTION
        }
    }

    public void remove()
    {
        i.remove();
    }

}

class EmptySubsetIterator extends SubsetIterator
{
    EmptySubsetIterator()
    {
        super(Collections.EMPTY_SET.iterator(), 0, 0);
    }
    
    public boolean hasNext()
    {
        return false;
    }
    
    public Object next()
    {
        throw new NoSuchElementException("This is an empty list."); //EXCEPTION
    }
    
    public void remove()
    {
        throw new IllegalStateException("next() will throw exception, it is "
                                        + "not possible to call this method."); //EXCEPTION
    }
}
